1. Field of the Invention
This invention relates to lights, and in particular, to warning lights requiring an elongated wide angle projection pattern for a beam radiating about a single defined spatial plane (hereafter referred to as the horizontal plane).
2. Related Prior Art
Emergency vehicles require their warning lights to have a wide beam pattern in the horizontal plane because it is necessary that approaching cars see the emergency vehicle regardless of their angle of approach. In addition, it is required that the wide angle beam be substantially uniform as bright and dark zones would prevent them from being reliably noticed. Finally, in order to reduce breakage and facilitate mounting, size and configuration restrictions usually apply to the design of these lighting devices. These restrictions create the need to produce a compact light that projects a wide beam.
Prior art has used a ribbed lens in front of the single parabolic reflector to permit the refractive properties of light to spread the beam into a wide beam pattern. Unfortunately, this system did not work efficiently for very wide beam patterns as the lens would require large variations in thickness to drastically bend the light rays. This type of design made the lens both expensive and fragile. In addition, the efficiency of the lens decreased as the required beam spread and corresponding lens thickness increased.
In U.S. Pat. No. 4,954,938 Lyons describes a wide angle lighting device consisting of a lamp, a complex reflector and an optical lens. The reflector consists of sections of three paraboloids of revolution. The central paraboloid with the light source at its focal point projects a central spot beam. The two wing paraboloids of revolution each also with the light source on their focal points project their own spot beams. The axis of revolution of each wing reflector is designed to intersect the axis of the central paraboloid with a given angle. Because the reflected rays are parallel to the axis of each parabola each wing projects its spot beam at that same given angle relative to the central beam. Lyons requires that the focal points of the wings coincide with the focal point of the central paraboloid and light source. This creates a design which prevents maximization of the beam spread for a limited size of the lighting device. A complex ribbed lens is added in a further attempt to spread the beams projected from the three reflectors and to reduce dark areas between the spot zones of the composite beam.
The prior art of Falge et al, relating to a vehicle head lamp, is found in U.S. Pat. No. 1,871,505. The Falge design was not a wide angle lighting device. Furthermore, it was based upon the use of a two filament lamp. It did nevertheless redirect the light beam downward by a second reflective surface.